It is frequently desired to provide signals corresponding to the colors of an image, for example in color television systems, color reproduction systems, etc. For this purpose, it is necessary to provide a light scanning arrangement that is sensitive to different colors. In one technique for producing such signals, a sensing array is provided having a plurality of light sensing devices, such a photodiodes, arranged to intercept light, for example from scanning optics. Different colored optical filters are arranged in the optical path of the light to the different sensors, so that the output of each sensor is responsive to light of a different color.
In the production of one form of color scanning device, as disclosed for example in U.S. Pat. No. 5,053,298, photodiode arrays are deposited in recesses in a substrate, and covered with a transparent planarizing layer. After a pattern conforming to predetermined ones of the diode arrays is lithographically formed on the surface of the planarizing layer, the planarizing layer is covered with a coloring agent to cover the pattern. The coloring agent is then removed from the surface of the planarizing layer, a protective layer is provided on the colored pattern, and the process is repeated to form other patterns of different color.
The above described process involves a number of photolithographic steps, and the precise alignment of the patterns with the respective diode arrays.
In another method for producing a color scanning device, as disclosed in U.S. Pat. No. 5,042,920, resin inks of different colors are printed on a transparent substrate in the form of patterns, such as stripes. In this process, the color patterns are overcoated with transparent electrodes of the same pattern. Pixel electrodes are formed on a second transparent substrate, and a sandwich is formed of these substrate assemblies, with a liquid crystal layer between the pattern electrodes and the pixel electrodes.
In each of the above techniques for providing color filters for a light scanning devices, the coloring agents are thus applied to external surfaces of the device, which are covered in the final preparation of the device, and the provision of the color filters is relatively complicated and costly.
Liquid color filters have been suggested for use in light sources, wherein color liquids are provided between glass plates, as disclosed e.g. in "Measuring Colour", R. W. G. Hunt, John Wiley & Sons, New York, 1987, pp 110-112, and "Redetermination of CIE Standard Source C", F. W. Billmeyer, Jr., Color research and applications, Volume 8. No. 2, Summer 1983, pp 90-96. These references are directed to devices of macroscopic dimensions (e.g. centimeters) wherein the absorption coefficients of the color liquids are low, for example 1000 times too low to provide effective color filtering in devices of microscopic dimensions, (e.g. of the order of micrometers) such as thin-film scan arrays.